The evolutionary development of the so-called 2nd generation mobile networks towards the so-called 3rd generation networks leads to network configurations where both, 2nd and 3rd generation radio access networks, operate with the same core network CN. In the first phase such 3rd generation radio access networks RAN will cover only hot spots, i.e. regions with high radio traffic load, later they will cover wider and wider areas.
Thus, radio transceiver devices will have to be introduced which will be able to operate with either of the radio access networks. This kind of radio transceivers is referred to as dual mode mobile stations MS.
In the GSM network two different accesses exist, i.e. GSM 900 and GSM 1800 However, the GSM 900 and 1800 dual access differs from the situation described above in that the GSM 900/1800 dual access offers the same services to the subscribers through both accesses, whereas in the 2nd/3rd generation dual access the difference between the two radio access methods and the development of the core packet network lead to a situation where the same services are not necessarily specified, not to mention implemented in both the 2nd and 3rd generation accesses. Even if the same services are specified, it may not be profitable nor reasonable to implement them in all networks.
There are several services that most probably will be supported by only one of the radio access network types. Such services are, for example, non-transparent circuit-switched services which are redundant in the 3rd generation radio access network, but which are widely used in the 2nd generation radio access network (GSM network).
Furthermore, transparent circuit-switched services are redundant in the 3rd generation radio access network, since the 3rd generation access network will be able to support a real-time packet transmission. On the other hand, transparent circuit switched services provide the only real-time service in GSM.
Moreover, real-time packet services are not available in GSM, whereas these services are available and important in the 3rd generation radio access network.
Thus, these circuit-switched services are very important in the current GSM networks. They will also be important in the foreseeable future because of their wide acceptance and introduction in the networks and because the forthcoming GSM packet service (GPRS) cannot support real-time transmission.
In contrast thereto, the 3rd generation network (UMTS, (universal mobile telephone system) will be able to support real-time packet transmission. This will make circuit-switched services redundant. Especially the implementation of the non-transparent circuit-switched services in the 3rd generation access will be questionable due to their redundancy, complexity and costs involved.
Thus, the dual mode mobile stations will have to operate in networks with various degrees of service support. Some 3rd generation accesses will support only packet services, some both packet services and transparent circuit switched services, some may even support both packet services and non-transparent circuit-switched services (if ever specified for 3rd generation radio access network). Some 2nd generation accesses will support only circuit-switched services, some both circuit-switched and (non-real-time) packet services.
Therefore, a new situation for the mobile stations arises. On the one hand, it is possible that a mobile station is attached to a 3rd generation cell and is requested (or requests itself) a service supported only by the 2nd generation access. Vice versa, it is also possible that a mobile station is attached to a 2nd generation cell and is requested (or requests itself) a service supported only by the 3rd generation access.
This leads to the drawback that in these situations only those services can be requested and used which are common to both a 2nd generation radio access network and a 3rd generation radio access network.
In addition, in case of services supported by both networks, there are several services which are supported with different qualities by different radio access networks. For example, the different radio access networks can provide different communication bit rates. Moreover, the price of connection can be different. For example, UMTS will be most probably more expensive in beginning, whereas later on GSM could be more expensive. Furthermore, the same services can be provided with different delays. In the prior art, these differences are not taken into account.
Thus, the above described drawbacks of the prior art result in a limited usability of a respective mobile station.